Manufacture of multiply-coiled electrodes for discharge devices



April 26, 1966 T. H. HEINE 3,247,699

MANUFACTURE OF MULTIPLY-COILED ELECTRODES FOR DISCHARGE DEVICES Filed Jan. 12, 1962 2 Sheets-Sheet 1 INVENTOR. THO/W6 5 H. Hf/NE.

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Apri !,-.26;"1966 T HEINE 3,247,699

H. MANUFACTURE OF MULTIPLY-COILED ELECTRODES Filed Jan. 12, 1962- FOR DISCHARGE DEVICES 2 Sheets-Sheet z DISSOLVABLE BUFFER WIRE 301 INVENTOR. THOMAS H. HE/NE United States Patent 3,247,699 MANUFACTURE OF MULTlPLY-COILED ELEC- TRODES FOR DTSCHARGE DEVICES Thomas H. Heine, Cedar Grove, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a

corporation of Pennsylvania Filed Jan. 12, 1962, Ser. No. 165,884 1t} Claims. (G. 72-371) This invention relates to electrodes for electric discharge devices and, more particularly, to an improved method of manufacturing multiply-coiled electrodes for fluorescent lamps and the like.

The design of fluorescent lamp cathodes, particularly those for so-called rapid and instant start lamps, presents an especially difficult problem in that such cathodes include a fine wire winding that heats up rapidly and must also have an overall structure massive enough to avoid localized overheating and sputtering. In addition, the electrode structure must be capable of holding a sufficient amount of electron-emission material to enable the lamps to have a long useful life.

The aforesaid stringent requirements are satisfied in the case of rapid and instant-start fluorescent lamps by utilizing an electrode that includes both a fine wire or so-called filament winding and a winding of much heavier wire. The fine wire is first wound around the heavier core wire and the resultant composite wire is then wound into a coil. This coil is, in turn, wound into a still larger coil to provide what is commonly referred to in the art as a triplewoun electrode. 'In reality, however, only the fine wire overwinding is triply coiled and the heavier wire is doubly coiled.

The desired large carrying capacity for emission mate rial is obtained by pairing a temporary filler wire with the core wire before the fine wire winding is applied and, after the subsequent coiling operations have been completed, chemically dissolving the filler wire and removing it from the coil structure. The fine wire accordingly is loosely draped around the core wire resulting in an electrode having a basket-like structure that can hold surprisingly large amounts of emission material. A triple-wound electrode of this character and the manner in which it is conventionally fabricated is disclosed in US. Patent No. 2,306,925, dated December 29, 1942.

Such triple-wound electrodes are difficult to manufacture and are expensive because the percent shrinkage during production is rather high. A large portion of the shrinkage arises from a defect known as abrasion. This term refers to the flattening and/or erosion of the fine wire which occurs as the core wire on which it is wound passes over the wire guides of the coil-winding machines and is subsequently wound around the mandrels during the secondary and tertiary winding operations. The abrasion is frequently severe enough to cause the fine overwinding to break. When this occurs large numbers of coils must be discarded insofar as the small hooks formed at the break causes the coils to become inseparably tangled, or the break allows the fine overwinding to become separated from the primary mandrel.

Moreover, experience has shown that the degree of abrasion increases as the diameter of the filament wire is decreased, or the diameter of the core wire is increased. Insofar as the highly-loaded high-wattage fluorescent lamps now being marketed require cathodes with finer filament wires and larger core wires, the resultant severity of the abrasion problem has made it extremely difficult to make cathodes for such lamps at a reasonable cost.

It is accordingly the general object of this invention to provide an improved method of making coiled electrodes that require a plurality of coiling operations.

3,247,699 Patented Apr. 26, 1956 A more specific object is the provision of a method of making triple-wound cathodes for fluorescent lamps that avoids the prior art difl'iculties and reduces the percent shrinkage and manufacturing cost of such cathodes.

Another object is the provision of a method whereby multiply-wound electrodes can be fabricated at higher production rates and with less material and imperfections compared to the prior art methods.

A further object is the provision of a method for making triple-wound cathodes that include combinations of fine filament wire and large core wires that were heretofore impractical from a manufacturing standpoint.

The aforesaid objects, and additional advantages which will appear as the description proceeds, are achieved in accordance with this invention by winding a larger wire along with the fine Wire around the primary mandrel dur ing the initial coiling operation and subsequently removing the larger wire from the finished coil. This larger wire, by virtue of its larger diameter, serves a buffer wire that protrudes beyond the fine wire and thus provides a temporary bearing surface that protects the fine wire from abrasion by the wire guides and mandrels during the subsequent coiling operations. The combination of such a butter wire with a pair of fine tungsten wires which are wound simultaneously as a group around the primary mandrel affords the additional advantages of decreasing the winding time and amount of buffer wire required, and maintaining a very uniform spacing between the fine wire turns in the finished electrode.

A better understanding of the invention will be obtained by referrring to the accompanying drawings, wherein:

FIGURE 1 is a perspective view of a mount for a 212 watt 96" highly-loaded fluorescent lamp which includes a triple-wound cathode manufactured in accordance with this invention;

FIGURE 2 is an enlarged side elevational view of the primary mandrel and coiling operation in accordance with one form of the invention;

FIGURE 3 is a cross-sectional view through the primary mandrel and winding along the line III-III of FIGURE 2, in the direction of the arrows;

FIGURE 4 is an enlarged fragmentary view, partly in section, of the secondary coil-and-mandrel assembly produced by the second coiling operation;

FIGURE 5 is a cross-sectional view through the secondary mandrel-and-coil assembly along the line V-V of FIGURE 4, in the direction of the arrows;

FIGURE 6 is a fragmentary side elevational view, partly in section, illustrating the tertiary coiling operation;

FIGURE 7 is a fragmentary elevational view on an enlarged scale of the tertiary mandrel-and coil assembly;

FIGURE 8 is a fragmentary view of one turn of the finished cathode, the adjoining portions of the cathode being shown in dotted outline and the emission coating being omitted for convenience of illustration;

FIGURES 9 and 10 are elevational and cross-sectional views, respectively, of the loosely overwound core wire employed in the finished cathode shown in FIGURE 8;

FIGURES 11 and 12 are views corresponding to FIG- URES 2 and 3 but illustrate an alternative method of making an electrode according to the invention; and,

FIGURES l3 and 14 are views corresponding to FIG- URES 9 and 10 but illustrate the multiple-wire overwind produced by the alternative method.

'While the present invention can be advantageously em- ,ployed to facilitate the manufacture of various types of coiled electrodes that require a plurality of coiling operations, it is especially adapted for use in fabricating triple-wound cathodes for fluorescent lamps and it has, accordingly, been so illustrated and will be so described.

With specific reference to the drawing, in FIG. 1 there o) is shown a mount for a 212 watt 96" highly-loaded rapid-start fluorescent lamp. The mount is of conventional design and, in general, consists of the usual glass flare 16 one end of which is press-sealed around a pair of lead wires 17 and 18. A heat-deflecting shield 19 is mounted on the press and connected to the lead wire 17. The ends of the lead wires that protrude from the stem press are fastened, as by clamping, to the ends of a triplewound electrode 24 and to a pair of enlarged anodes 21 and 22 disposed on either side of the electrode. The primary and secondary turns of the electrode are filled with a suitable electron-emissive material such as the well-known alkaline earth carbonates, applied in the usual manner, to activate the electrode and permit it to function as a cathode.

THE INVENTION The deformation and abrasion of the fine filamentary wire winding during manufacture is preferably eliminated in accordance with this invention by winding a buffer wire of larger diameter simultaneously and in side-byside relationship with the fine wire during initial or primary coiling operation. This operation is illustrated in FIGS. 2 and 3. As there shown, a pair of primary wires consisting of a very fine wire or so-called filament wire 28 of tungsten and a buffer wire of larger diameter and dissimilar metal, such as molybdenum, are wound in contiguous side-by-side relation around a tungsten core wire 24 and a temporary filler wire 26 of molybdenum. The core wire is of smaller diameter than and is disposed in parallel longitudinally-extending paired relationship with the aforementioned filler wire to provide a composite primary mandrel. The paired fine filamentary and buffer wires are wound around the composite primary mandrel at a pitch such that the turns of grouped wires lie next to one another as shown in FIG. 2. The tungsten core wire and filler wire together with the tight overwinding of paired filament and buffer wires constitute a first multiple-strand or composite wire 23, as indicated by the bracket in FIG. 2. This initial coiling operation can very readily be performed on a continuous-winding type coiling machine that has been modified to include two rather than the usual single bobbin.

Alternatively, instead of winding the fine filamentary wire 28 and buffer wire 30 simultaneously around the composite primary mandrel as above described, the filamentary wire could be wound first in the conventional manner and the buff-er wire wound later, or even on another coil-winding machine. Thus, the invention includes wtihin its scope both the simultaneous and sequential winding of the additional buffer wire 30.

Moreover, the tungsten core wire 24 does not necessarily have to be smaller than the filler wire 26 as here shown, but may be of the same diameter as or even larger than filler wire, depending upon the electrode design, etc.

As indicated in FIGS. 2 and 3, the diameter of the buffer wire 30 exceeds that of the fine filamentary wire 28 by a distance d. The filamentary wire winding is, accordingly, recessed behind the buffer wire winding a corresponding distance and is thus protected from abrasion during the subsequent coiling operations hereinafter described.

After the initial or primary winding operation has been completed the resulting first composite wire 23 is wound, as by another continuous coil-winding machine, around a larger secondary molybdenum mandrel. This secondary coiling operation produces a second and much larger composite wire 42, which is indicated by the bracket in FIG. 4. As shown, the secondary mandrel 36 is larger than either the filler or core wire and the pitch of the secondary winding is such that there is a predetermined spacing between the turns of the first composite wire 23.

As shown more particularly in FIG. 5, the buffer wire 30 by virtue of its larger diameter protrudes beyond the fine filament wire 28 and prevents it from coming into contact with the secondary mandrel 36. The larger diametered buffer wire, accordingly, serves as a temporary bearing surface that completely eliminates the abrasion or flattening of the fine wire overwinding that would otherwise occur as the composite wire 23 is tightly wound around the secondary mandrel 36 during the secondary coiling operation.

The same protection of the fine filamentary winding 28 against abrasion is also afforded .by the buffer wire 30 during the tertiary coiling operation, which is depicted in FIG. 6. As shown, the second composite wire 42 (that is, the first composite wire 23 and the secondary mandrel 36) is fed from a bob-bin (not shown) through the holder 32 and coiling die 34 of another coil-winding machine and then over and around a guide 38, at which point it is wound around a third and considerably larger steel mandrel 44. In order to reduce friction between the second composite wire 42 and the coiling die 34 the guide 38 preferably comprises a miniature or so-called microball bearing that is free to rotate about a pin 40 secured to the holder. A detailed description of this type of coil feed assembly and a tertiary winding operation of this character is set forth in U.S. Patent No. 2,783,816 dated March 5, 1957 and owned by the assignee' of the present invention.

As a result of the tertiary winding operation a triplewound or compound coil having at least one turn is formed. In the particular type of cathode 20 shown in FIG. 1, the coil has five major turns. This third coiling operation is preferably done on a retractable-type coilwinding machine wherein the mandrel 44 is mechanically withdrawn from the coil after it is formed, as indicated by the arrow in FIG. 6. By way of clarification, the convolution of the second composite wire 42 illustrated in broken outline in FIG. 7 corresponds to a single turn of the finished cathode 20 shown in FIG. 1.

As will be noted in FIG. 7, the differential (dimension d between the diameter of the primary filament wire 28 and primary buffer wire 30 also serves to protectively isolate the fine filament wire from the retractable mandrel 44- during the tertiary coiling operation and eliminates any abrasion of the filament wire that would otherwise occur during this phase of manufacture. Since the outermost surface of the buffer wire will always protrude beyond that of the fine wire, the latter will always be protected from damage regardless of how many coiling operations are performed.

After the compound coil is formed it is cut from the uncoiled portion of the composite wire 42 while the coil is still on the tertiary-winding machine. The resulting partly-fabricated electrodes at this stage of fabrication are of the same size and configuration as the finished cathde 20, except that they still contain the molybdenum filler wire 26, buffer wire 30 and secondary mandrel 36 and are not coated with emission material.

The aforementioned partly-fabricated electrodes are then further processed by annealing them in dry hydrogen for about 10 minutes at about 1200 C. in order to set the various windings in place on the mandrels. The electrodes are then immersed in a suitable solution that dissolves molybdenum, such as a mixture of nitric and sulfuric acids, to remove the filler and buffer wires and the secondary mandrel. Since the latter are all fabricated from mloybdenum they are all removed in a single operation. The first composite wire 23 is thus converted into an entirely different composite wire 23' consisting of the tungsten core wire 24 and a loose overwind of tungsten filament wire 28, as shown in FIG. 8. The turns of the finished cathode 20, part of which is illustrated in this figure, accordingly consists of a continuous triply-coiled filament wire supported by a heavier doubly-coiled corewire that extends through the convolutions of the filament wire.

The basic structure of the wire 23' that forms the finished electrode is shown in greater detail in FIGS. 9 and 10. As shown, the removal of the filler wire 26 causes the tungsten filament wire 23 to become loosely draped around the tungsten core wire 24. This provides a basketlike structure capable of holding large amounts of emission material. The removal of the interposed butler wire 30 from the fine wire winding spaces the turns of the latter a uniform distance apart, as denoted by the dimension S in FIG. 9. The buffer wire thus serves the dual purpose of eliminating abrasion defects in the finished electrode and maintaining a very uniform spacing between the turns of the fine wire filament or overwind.

It should be noted that the partly-fabricated electrodes, that is, those containing the molybdenum filler and buffer wires and secondary mandrel, may be shipped in this form from the coil-winding department to the factory or the lamp manufacturing department where the final dissolving operation can be performed. The term partlyfabricated electrode as here used refers to the compound coils produced by the tertiary-coiling operation. At this stage of fabrication these compound coils comprise the fine filamentary wire 23 and larger buffer wire 30 disposed in sideaby-side relation and wound into a tight coil that is, in turn, wound into a second and larger coil which is then wound into a third and still larger coil. The final coil still contains the molybdenum filler wire26 which, together with the core wire 24, is located within and extends through the turns of the first coil. The secondary molybdenum mandrel 36 is also still in place within and extends through the turns of the second coil.

I. Specific example 'Following is a specific example of a cathode of the type used in a 212 watt 96" highly-loaded fluorescent lamp 1 /2 inches in diameter operating at 1.5 amp. arc current whichwill illustrate in greater detail how this invention may be practiced. In this particular case a 1 mil tungsten filament. Wire 28 and a 1.5 mil molybdenum buffer wire 36 are wound in paired relation around a 5.3 mil tungsten core wire 24 and a mil molybdenum filler wire 26 at about 380 turns per inch (TF1). The resulting composite wire was then wound around a 13 mil secondary molybdenum mandrel 36 at about 42 TPI. The resulting second composite wire was then wound around a steel retractable mandrel 50 mils in diameter at about 17 to 21 TPI.

ALTERNATIVE EMBODIMENT It has been found that the amount of buffer wire required per electrode can be drastically reduced and the primary winding speed can be greatly increased by properly combining one buffer wire with two fine filamentary wires and winding all three wires simultaneously around the primary composite mandrel. This embodiment is illustrated in FIGS. 11 and 12 and, as there shown, consists of locating the larger diametered buffer wire 3M1 between and in contiguous side-by-side relation with a pair of tungsten filament wires 2dr: and 28b and winding all three wires as a group around the paired tungsten core wire 24a and the larger molybdenum filler wire 26a to form a first composite wire 45. This group of three primary wires is wound around the composite primary mandrel at about half the turns per inch compared to that at which the pair of primary wires were wound in the first embodiment so that a predetermined spacing S exists between adjacent turns of the grouped primary wires, as shown in FIG. 11. Preferably, the spacing S is made approxiand tertiary coiling operations and finally the dissolving operation as described above in connection with the first embodiment.

The basic stlucture of the Wire 45 in the finished electrode produced in accordance with 'this embodiment is illustrated in FIGS. 13 and 14. As shown, the tungsten core wire 24a is loosely overwound with the pair of fine tungsten filamentary wires 28a and 28b, the adjacent turns 'whereof are spaced from one another a uniform distance S The distance X between adjacent turns of the same tungsten wire is equivalent to twice the diameter of the butler-wire 3011 plus the diameter of the filamentary Wire, as will be obvious from FIGS. 11 and 13. This uniform spacing is obtained by making the spacing S between turns of the three-wire primary grouping approximately equal to the buffer wire diameter.

When the filler wire 26a and buffer wire 3tia are dissolved out of the coil the pair of fine tungsten filamentary wires 28a and 2812 are loosely draped around the core wire 24a, as shown in FIGS. 13 and 14. Thus, the basic structure of the wire 45' in the finished coil is identical to that produced with an overwinding of a single tungsten wire, except that two fine wires encircle the core wire at about twice the pitch. The filamentary tungsten wires are connected in parallel with one another when mounted on the lamp stem by the shunting effect of the lead wire clamp. The electrical resistance of this type electrode is, accordingly, lower than when a single filamentary wire is used.

It will be noted that since only one buffer wire is used for each pair of filamentary tungsten wires only half as much buffer wire is required per coil as when one buffer wire is used for each filamentary wire. In addition, since the three wires are wound at twice the pitch the primary winding speed is doubled. Thus, combining one buffer wire with a pair of filamentary tungsten wires in accordance with this form of the invention not only provides a finished electrode with improved electrical characteristics but also effects a substantial cost reduction by decreasing the amount of buffer wire required and by increasing the rate of production.

As will be obvious to those skilled in the art, the required number of primary wires can very readily be Wound simultaneously around the primary mandrel simply by increasing the number of bobbins and wire guides on the coil-winding machine.

II. Specific example Following is a specific example of the wire sizes and coiling datafor a particular type coil further illustrating the above-described alternative embodiment.

Satisfactory 212 watt coils for a rapid-start highlyloaded fluorescent lamp 8 feet long and 1 /2 inches in diameter have been made according to this method by simultaneously winding a pair of filamentary tungsten wires 1 mil in diameter and a 1.5 mil molybdenum buffer wire as a group in side-by-side contiguous relation around a paired 5.3 mil tungsten core Wire and a 10 mil molybdenum filler wire. The filamentary-bufier wire grouping was wound at TPI. The resulting composite wire was then wound around secondary and tertiary mandrels of the same sizes and in the same fashion as set forth above in the first specific example.

The term pitch as used in this description refers to the distance between identical points on adjacent turns of a given coil and is equal to l/TPI.

In summary, the objects of the invention have been achieved insofar as a method has been provided wherein a multiply-coiled electrode having an overwinding of fine I wire can be made without abrading or otherwise damaging the fine wire winding. "The improved process also maintains a very uniform spacing of the fine wire turns and can be very easily modified to effect a considerable reduction in manufacturing costs.

While several examples of the improved method of coil manufacture have been described in detail, various modifications in the procedure may be made without departing from the spirit and scope of the invention.

I claim:

1. The method of making a coiled electrode, comprising winding a pair of primary wires of dissimilar metals and diameters around and in side-by-side relation on a first composite mandrel comprising an electrode core wire and a filler wire of dissimilar metals, winding the resulting first composite wire around a second mandrel to form a second composite wire, winding said second composite wire around a third mandrel to form a compound coil having at least one turn, and then removing the larger one of said primary wires, said filler wire and said second and third mandrels from said coil.

2. The method of making a coiled electrode as set forth in claim 1 wherein said primary wires are wound in contiguous side-by-side relation on said first composite mandrel.

3. The method of making a coiled electrode as set forth in claim 1 wherein said filler wire, the larger one of said pair of primary wires, and said second mandrel are each fabricated from the same refractory metal and are chemically removed from the coil after the third coiling operation is completed.

4. The method of making a coiled electrode, comprising simultaneously winding 21 pair of tungsten filament wires and a larger buffer wire of molybdenum around and in side-by-side relation on a first composite mandrel comprising a tungsten core wire and a molybdenum filler wire disposed in longitudinal paired relationship, winding the resultant first composite wire on a second mandrel of refractory metal to provide a plurality of spaced turns thereon and form a second composite wire, winding said second composite wire around a third mandrel to form a compound coil having at least one turn, mechanically withdrawing said third mandrel from said compound coil, severing said compound coil from the uncoiled portion of said second compo-site Wire, and then chemically dissolving said molybdenum buffer and filler wires and said second mandrel to remove them from said coil.

5. The method of making a coiled electrode as set forth in claim 4 wherein said second mandrel is fabricated from molybdenum and is chemically dissolved and removed from the compound coil along with said molybdenum buger and filler wires.

6. In the manufacture of a coiled electrode that involves a plurality of coiling operations and includes a core wire having a loose overwind of fine wire therearound, the steps of: simultaneously winding said fine wire and a larger buffer wire of dissimilar metal in paired relationship around a composite mandrel that includes said core wire and a filler wire of dissimilar metal to provide a plurality of turns of said paired wires on said composite mandrel, whereby said buffer wire by reason of its larger dimension relative to said fine wire serves as a temporary bearing surface that protrudes beyond and protects the fine primary Wire from abrasion during subsequent coiling operations; and then chemically removing said buffer and filler wires from the electrode structure after all of the coiling operations have been completed.

7 In the manufacture of a coiled electrode that involves a plurality of coiling operations and includes a core wire having a loose overwind of fine filamentary wire therearound, the steps of: winding a pair of fine filamentary wires and a centrally-disposed buffer wire as a group in side-by-side relation around a composite primary mandrel that includes said core wire and a filler wire thereby to provide a plurality of spaced turns of said grouped wires on said composite mandrel; said centrally disposed buffer wire being larger and fabricated from a different metal than said pair of filamentary wires and, by reason of its larger dimension, providing a bearing surface that protects the filamentary wires from abrasion during the subsequent coiling operations; and then, after all of the coiling operations have been completed, chemically removing said buffer wire from the electrode structure.

8. The method of making a coiled electrode as set forth in claim 7 wherein the grouped filamentary and buifer wires are wound around the composite primary mandrel at a pitch such that the spacing between adjacent turns of said grouped wires is approximately equal to the diameter of the buffer wire.

9. The method of making a coiled electrode as set forth in claim 7 wherein; said filamentary wires and buffer wires are simultaneously wound around the composite primary mandrel, in contiguous side-by-side relation and said buffer wire and filler wire are both fabricated from molybdenum and are simultaneously chemically dissolved and removed from the electrode structure after all of the coiling operations have been completed.

10. -In the manufacture of a coiled electrode that involves a plurality of coiling operations and includes a tungsten core wire having a loose overwind of tungsten filament wire therearound, the steps of: winding a pair of tungsten filament wires and a molybdenum buffer wire as a group around a composite mandrel that includes said core wire and a molybdenum filler wire thereby to provide a plurality of spaced turns of said grouped wires on said composite mandrel; said buffer wire being larger than and located between said filament wires in side-byside relationship therewith and, by virtue of its larger diameter, providing a bearing surface that protects said filament wires from abrasion during the subsequent coiling operations; adjusting the pitch at which the filament and buffer wire grouping is wound to provide a predetermined spacing between adjacent turns of said grouped wires; and then simultaneously chemically dissolving said buffer and filler wires and removing them from the electrode structure after 'all of the coiling operations have been completed.

References Cited by the Examiner UNITED STATES PATENTS 2,067,746 1/1937 Zabel 29-423 2,175,345 10/1939 Gaidies et a1. 2925.l7 2,218,345 10/1940 Spaeth 7l.5 2,225,239 12/1940 Spaeth 313344 2,258,158 10/1941 Lowry 313344 2,306,925 12/1942 Aicher 14071.5 2,359,302 10/1944 Curtis 2925.l5 2,516,930 8/1950 Varian 29423 2,870,520 1/1959 Desvignes 2925.17

RICHARD H. EANES, 1a., PrimaryExaminer.

LEON PEAR, Examiner. 

1. THE METHOD OF MAKING A COILED ELECTRODE, COMPRISING WINDING A PAIR OF PRIMARY WIRES OF DISSIMILAR METALS AND DIAMETERS AROUND AND IN SIDE-BY-SIDE RELATION ON A FIRST COMPOSITE MANDREL COMPRISING AN ELECTRODE CORE WIRE AND A FILLER WIRE OF DISSIMILAR METALS, WINDING THE RESULTING FIRST COMPOSITE WIRE AROUND A SECOND MANDREL TO FORM A SECOND COMPOSITE WIRE, WINDING SAID SECOND COMPOSITE WIRE AROUND A THIRD MANDREL TO FORM A COMPOUND COIL HAVING AT LEAST ONE TURB, AND THEN REMOVING THE LARGER ONE OF SAID PRIMARY WIRES, SAID FILLER WIRE AND SAID SECOND AND THIRD MANDRELS FROM SAID COIL. 